Sir John Clifford Mortimer (born 21 April 1923) is an English barrister turned prolific writer and dramatist. His oeuvre includes over fifty books, plays, and scripts. The play, A Voyage Round My Father (1971) is autobiographical, recounting his experiences as a young barrister and his relationship with his blind father.

Mortimer's most famous creation is a character named Horace Rumpole, a barrister whose specialty is defending those accused of crime in London's redoutable hall of justice, the Old Bailey. Mortimer created Rumpole for "Rumpole of the Bailey", a 1975 episode of Play For Today ; Played with gusto by Leo McKern, the character proved popular, and was spun off into a Rumpole of the Bailey television series for Thames Television and a series of books (all written by Mortimer). In September - October 2003, BBC Radio 4 broadcast 4 new 45-minute Rumpole dramatizations by Mortimer starring Timothy West in the title role.

In August 2004 he became a father when he met his son Ross Bentley, more than 40 years after a secret affair with Wendy Craig. The son was brought up by Craig and her husband, Jack Bentley, the show business writer and musician. In Mortimer's memoirs, Clinging to the Wreckage , he wrote of "enjoying my mid-thirties and all the pleasures which come to a young writer."

John Mortimer has five children, Sally Silverman , Jeremy Mortimer , Ross Bentley , Emily Mortimer, Rosie Mortimer and is married his second wife Penny Mortimer who he lives with just outside Henley.